Digital-to-analog (D/A) converters are found in a wide variety of electronic circuit applications. An analog output of a D/A converter is used by analog circuitry which requires a predetermined amount of analog signal strength to operate. However, most D/A converters do not have the ability to provide a sufficiently strong analog output signal to be used by conventional analog circuits. Therefore, driver circuits which drive low impedance outputs, also known as line drivers, are used with D/A converters to drive the output of the D/A converter to a signal level which is sufficient to be used by other analog circuits. The line driver must be able to drive low impedance loads without degrading stability. It would be desirable for it to operate from low supply voltages, use little quiescent current, and layout in a small area.
Existing analog output stages for line drivers which are noted in an article "MOS Op Amp Design - An Overview" by Gray and Meyer in IEEE Journal of Solid-State Circuits, Vol SC-17, No. 6, Dec. 1982, pp. 969-982, have several disadvantages. One of these disadvantages is frequency instability resulting from a multiple pole characteristic. This feature which exists in many analog line drivers can cause the driver to inadvertently oscillate at certain frequencies. The stability of the driver varies due to random fluctuations in the manufacturing process of the integrated circuit. Because of processing fluctuations, the circuit's poles may need to be compensated for with additional components in the circuit, adding complexity and cost. In addition, when the output of a line driver is near the signal ground reference, either output node feedback to the last transistor stage or transistor threshold voltage mismatch or both may cause significant quiescent currents in known driver circuits. Since quiescent currents exist while the circuit is in a standby mode, significant unwanted power dissipation occurs.